The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A multi-speed transmission uses a combination of clutches, planetary gear arrangements, and fixed interconnections to achieve a plurality of gear ratios. In one example, friction type clutches are used in the transmission, and are selectively engaged to achieve a particular gear ratio. However, when disengaged, the friction clutches tend to produce drag when there is relative motion between the clutch input member and output member, which can lead to decreased fuel economy.
In an effort to improve fuel economy, a one-way clutch may be employed instead of a friction clutch to transmit power from a first input member to a second driven member. The one-way clutch transmits torque in a first direction and releases or decouples in a second, opposite direction. Once released, the driving member is free to rotate in the second opposite direction relative to the first direction, and the one-way clutch can overrun or freewheel. This allows the vehicle to travel in a coasting or gliding mode where the drivetrain is decoupled from the engine, thus eliminating any losses associated with the drivetrain turning the engine.
Engine braking occurs when torque to the driving member is reduced, the driving member and the driven member remained coupled to one another, and back torque as a result of turning the engine with reduced power and pumping forces is transmitted in an effort to reduce the speed of the driven member. However, freewheeling the one-way clutch decouples the driven and the driving member, thereby making engine braking not possible. Thus, engine braking in a vehicle operated with a one-way clutch will not work unless additional components are included, such as an additional clutch to selectively couple the driving member and the driven member.
Thus, while current transmissions achieve their intended purpose, there is a need for a new and improved transmission which exhibits improved performance while allowing engine braking.